This invention relates generally to radar altimeters, and more specifically to a radar altimeter with forward obstacle avoidance capabilities.
The proper navigation of an aircraft in all phases of its flight is based to a large extent upon the ability to determine the terrain over which it is passing, and further the ability to determine a position of the aircraft. In this regard, instrumentation, radar systems, and specifically, radar altimeters are used in combination with accurate electronic terrain maps. Radar altimeters, in conjunction with the electronic terrain maps, which provide the height and location of objects on the map, aid in the flight and the planning of a flight path for the aircraft.
Radar altimeters are commonly implemented within aircraft. A radar altimeter typically includes a transmitter for applying pulses of electromagnetic energy at regular intervals to an antenna which then radiates the energy, in the form of a transmit beam, towards the earth""s surface. A transmit beam from a radar is sometimes said to xe2x80x9cilluminatexe2x80x9d an area (e.g. the ground) which reflects the transmit beam.
The radar altimeter further includes a signal receiver which receives the reflected pulses, sometimes referred to as return pulses, an echo, or as a return signal. Return pulses are received at a receive antenna, and constitute transmit beams that have been reflected from the earth""s surface. It is known that some radar altimeters utilize a single antenna for both transmitting and receiving. A closed loop servo tracker for measuring the time interval between the transmitted pulse and its associated return pulse also forms a part of the radar altimeter. The time interval between the transmit pulse and the return pulse is directly related to the altitude of the aircraft above the highest object on the ground that is reflecting the transmit pulses.
However, when flying at very low altitudes certain terrain features in front of the aircraft, in the flight path, may not be detected. Known radar aircraft altimeters generally do not detect objects in front of an aircraft flight path. Examples include, for example, tall buildings, or the side of a cliff.
Therefore an aircraft equipped with a radar altimeter can determine an altitude, but the aircraft is generally not able to recognize objects in front of it unless it is also equipped with, for example, a costly scanning laser radar. In addition to being costly and relatively heavy, which is always an issue for air vehicles, such scanning laser radars are sometimes ineffective, for example, when encountering one or more of rain, snow, fog, dust, and smoke.
In one aspect, a radar altimeter is provided that comprises a transmitter for transmitting a radar signal toward the ground, a receiver for receiving a reflected radar signal from the ground, and at least one altimeter antenna coupled to one or both of the transmitter and receiver. The radar altimeter also comprises a forward facing millimeter wave (MMW) antenna configured to move in a scanning motion, and a frequency up/down converter coupled to the MMW antenna, the transmitter, and the receiver. The converter up converts a frequency received from the transmitter to a MMW frequency and outputs the MMW frequency to the MMW antenna, and down converts a frequency received at the MMW antenna to a radar frequency, outputting the radar frequency to the receiver. The radar altimeter also comprises a radar signal processor coupled to the transmitter, to the receiver, and to the MMW antenna. The processor controls the scanning motion of transmissions from the MMW antenna, processes signals received at the altimeter antenna for a portion of the scanning motion, and processes signals received at the MMW antenna for other portions of the scanning motion.
In another aspect, a method of operating a radar altimeter to provide forward obstacle notifications is provided. The altimeter includes a forward facing millimeter wave (MMW) antenna, a frequency up/down converter coupled to processing circuits of the radar altimeter and MMW antenna, and altimeter transmit and receive antennas coupled to the processing circuits. The method comprises causing transmissions from the MMW antenna to move in a scanning motion, the scanning motion having horizontal portions and turnaround portions at ends of the horizontal portions, transmitting, receiving, and processing signals at the MMW antenna during the horizontal portions of the scanning motion, and transmitting, receiving, and processing signals at the altimeter transmit and receive antennas during the turnaround portions of the scanning motion.
In still another aspect, a radar altimeter comprising a forward obstacle warning unit is provided. The forward obstacle warning unit comprises a frequency up/down converter and a millimeter wave (MMW) antenna coupled to one another. The MMW antenna transmits signals received from the frequency up/down converter which originate at a transmitter of the radar altimeter. The frequency up/down converter receives signals from the MMW antenna, reduces the frequency, and passes the frequency reduced signals to a receiver of the radar altimeter.
In yet another aspect, a method for incorporating a forward obstacle warning feature into a radar altimeter is provided. The radar altimeter includes a forward obstacle warning unit including a circulator coupling a forward facing millimeter wave (MMW) antenna to a frequency up/down converter, the forward obstacle warning unit also coupled to a transmitter and receiver of the radar altimeter through respective transmit and receive switches. The transmitter and receiver are also coupled to at least one radar antenna through the transmit and receive switches for an altimeter function. The method comprises controlling a position of transmissions from the MMW antenna utilizing a processor of the radar altimeter, processing radar returns received at the MMW antenna to determine a range to a forward object, and processing radar returns received at the radar altimeter antenna to determine an altitude.